1. Field of the Invention
This invention relates to a novel transition-metal compound having a bis-substituted-cyclopentadienyl ligand of bridged structure. The compound of the present invention is useful as a catalyst component for stereo-regular olefin polymerization.
2. Description of the Related Art
As a homogeneous catalyst for olefin polymerization, the so-called Kaminsky catalyst (metallocene compound/aluminoxane) has been well known. The catalyst has a very high polymerization activity, and in the case of propylene polymerization, it has also been known that it is possible to produce both of atactic polypropylene (Makromol. Chem. Rapid Commun. 4,417-421 (1983), Japanese patent application laid-open Nos. Sho 58-19,309/1983, Sho 60-130,604/1985 and Sho 61-211,307/1986) and isotactic polypropylene (Angew. Chem. Int. Ed. Engl. 24,507-508 (1985), J. Am. Chem. Soc. 1984, 106, 6355-6364, Japanese patent application laid-open No. Sho 61-264,010/1986, J. Am. Chem. Soc., 1987, 109, 6544-6545 and Japanese patent application laid-open No. Sho 63-66206/1988), in the presence of the above catalyst.
In the case of metallocene compounds, transition-metal compounds having a bis-unsubstituted-cyclopentadienyl ligand crosslinked with silicon, phosphine, amine or carbon are known (Japanese patent application laid-open No. Sho 62-296,008/1987), and as to zirconium or hafnium compounds, dimethylsilylbis(cyclopentadienyl)zirconium or hafnium dichloride has been synthesized (Z. Naturforsch, 38b, 321-325 (1983) and Inorg. Chem. 1985, 24, 2539).
Further, as to preparation examples of transition-metal compounds having a ligand using substituted-cyclopentadienyl rings crosslinked with silicon, dimethylsilylbis(methylcyclopentadienyl)titanium dichloride (Monatsh. Chem. 112,887-897 (1981)), dimethylsilylbis(t-butylcyclopentadienyl)scandium hydride (J. Am. Chem. Soc. 1988, 110,976-978), Me.sub.2 Si(Me.sub.4 C.sub.5)MCH[SiMe.sub.3 ].sub.2 (M=Nd, Sm, Lu) type compounds (J. Am. Chem. Soc. 1985, 107, 8103-8110), etc. have been known.
However, with regard to zirconium compound or titanium compound, an example of those having a dimethylsilylbis(tetramethylcyclopentadienyl)ligand has been known (Chem. Ber. 119, 1750-1754 (1986)), but preparation example of compounds having a ligand using other substituted-cyclopentadienyl rings crosslinked with silicon or germanium has never been reported. Much less, any concrete practical example wherein olefins are polymerized using such compounds to obtain isotactic polymers has also never been reported.